Pigment inks generally produce printed matter with better image fastness than do dye inks, and are used in a variety of applications that take advantage of this feature, such as wide-format color inkjet recording inks aimed at the signage and display market. In this color inkjet recording, various hues are usually expressed by using a three-color ink set comprising three colors of pigment ink (yellow (Y), magenta (M), and cyan (C)), which are the primary colors in subtractive color mixing, or a four-color ink set that adds to black (K) to these.
However, problems with the above-mentioned three- and four-color ink sets include a narrow color reproduction range and a decrease in the saturation of printed portions of secondary and higher color (mixed color portions), and such ink sets have yet to reach the level of being able to provide printed matter of high image quality comparable to that of silver halide photography, lithographic printing, and so on.
Some of the ways for dealing with the decrease in saturation have included increasing the pigment concentration of the various YMC inks, and increasing the amounts in which the YMC inks are applied to the recording medium, in an effort to boost saturation. All these methods, however, had drawbacks in that they led to a decrease in gloss and that a photographic look could not be obtained even when glossy paper was used as the recording medium. Also, to efficiently spread out the saturation with just three primary color (YMC) inks, a type of pigment intended for use with YMC inks having ideal spectral characteristics suited to subtractive color mixing has to be selected, and furthermore there are only a few types of pigment that also have excellent light resistance, gas resistance, and so forth, and even if one of these few types is used in an attempt to raise saturation by an increase in pigment concentration as mentioned above, there is the danger that this will cause problems such as nozzle clogging in an inkjet printer or hue changes of the three primary colors, so this approach is not effective.
Japanese Laid-Open Patent Application 2000-351928 discloses a pigment ink set with a wide color reproduction range, in which a color printing-use color inkjet ink set comprises orange, green, and/or violet, each containing a specific pigment, in addition to the three YMC pigment inks (Patent Document 1). This ink set, though, had a saturation reproduction range that could not be considered adequate, and it was impossible to raise the saturation without leading to a decrease in glossiness. In particular, it was impossible to raise the vermilion saturation without leading to pronounced granularity when the image was expressed by dots (that is, the dots were visible to the naked eye as particles). WO99/05230 discloses an ink set comprising two special color pigment inks (orange and green) in addition to YMCK four-color pigment inks (Patent Document 2), but although this ink set does have excellent reproducibility of colors with low saturation and high brightness, such as pastel colors, its saturation reproduction range is just as inadequate as the above-mentioned ink sets when it comes to other colors, making it impossible to raise the saturation without leading to a decrease in glossiness.
Another problem with recorded matter formed using a conventional pigment ink set was that the hue of the recorded image changed with the illuminating light source, which is called metamerism. This metamerism was particularly pronounced in composite blacks and grays formed with a YMC three-color ink, and was a source of diminished image quality.
Various ink sets have been proposed in an effort to solve these problems encountered with conventional ink sets, such as an ink set comprising a specific special color pigment ink (red and/or violet) in addition to the three YMC pigment inks in order to provide printed matter with high saturation and gloss and without any particularly pronounced granularity, but the effect thereof has yet to reach a satisfactory level. The reason lies in the problem that the improvement varies with the type of recording medium to which the ink set is applied. For instance, when the ink set is applied at low resolution to a recording medium having a coating layer, such as photographic paper, the problem is that granularity becomes particularly pronounced because dot expression is employed in the recording. When the ink set is applied to plain paper (a recording medium in which fibers are exposed on the recording surface), the problem is that there is a particular decrease in coloration of dark areas (where the L* value defined in the CIE Lab color space on the recording medium is around 40).
Depending on the image being formed, its reflected light may not consistently be white, and instead may appear to reflect in another color, which diminishes the quality of the image. Consequently, there has been a need for the development of an ink set capable of reflecting white light from an image.                Patent Document 1: Japanese Laid-Open Patent Application 2000-351928        Patent Document 2: WO99/05230        
It is therefore an object of the present invention to provide an ink set with which can be obtained a glossy recorded image that has a wide color reproduction range, has high saturation, and has no pronounced granularity caused by dot expression, and in particular with which can be obtained a recorded image that has greatly suppressed granularity caused by dot expression when applied to a medium having a coating layer, and that has outstanding coloration when applied to plain paper.
It is a further object of the present invention to provide the following ink sets (1) to (6) that add to the excellent performance described above.
(1) An ink set capable of giving a high-quality image with reduced metamerism and with white reflected light of the image.
(2) An ink set capable of giving a high-quality image with reduced metamerism and with excellent expression of high-saturation magenta color.
(3) An ink set capable of giving a high-quality image with reduced metamerism and with excellent coloration of dark areas of a specific hue angle on plain paper.
(4) An ink set capable of giving a high-quality image with reduced metamerism and with excellent expression of high-saturation orange-red color regions.
(5) An ink set capable of giving a high-quality image with good gas resistance and capable of expressing low-brightness and high-saturation orange and red at the same time.
(6) An ink set capable of giving a high-quality image with white reflected light of the image and suppressed fading.
It is another object of the present invention to provide an ink set of high reliability for use in inkjet recording.
It is yet another object of the present invention to provide a recording method and recording system with which can be obtained a glossy recorded image that has a wide color reproduction range, has high saturation, and has no pronounced granularity caused by dot expression, and in particular with which can be obtained a recorded image that has greatly suppressed granularity caused by dot expression when applied to a medium having a coating layer, and that has outstanding coloration when applied to plain paper.
It is still another object of the present invention to provide recorded matter having a glossy recorded image that has a wide color reproduction range, has high saturation, and has no pronounced granularity caused by dot expression, and in particular has greatly suppressed granularity caused by dot expression when applied to a medium having a coating layer, and has outstanding coloration when applied to plain paper.